Depends on how much you smoke at one time.

Bottom line, holding it in for more than several seconds is going to irritate your lungs more, and probably won't even make much of a difference in how you feel if you are smoking at least a bowl or two.

But try this some day (if you can lol)- take ONE hit and stop there. Literally one hit and hold it as long as you can. See how high you get. The next time you smoke (on a different day, make sure each time that it's the first smoke of your day), take ONE hit again, same size hit, same weed, same smoking method; only this time, hold it for just a few seconds. Tell me if there is not a significant difference in how you feel

It's all relative to the total amount consumed. The more you hit in one session, the less significant the gain from holding each one longer becomes.